Many fabrics are made from synthetic fibers. Conventionally, two processes are used to manufacture synthetic fibers: a solution spinning process and a melt spinning process. The solution spinning process is generally used to form acrylic fibers, while the melt spinning process is generally used to form nylon fibers, polyester fibers, polypropylene fibers, and other similar type fibers. As is well known, an acrylic fiber includes a long-chain synthetic polymer characterized by the presence of acrylonitrile units, a nylon fiber includes a long-chain synthetic polyamide polymer characterized by the presence of an amide group —CONH—, a polyester fiber includes a long-chain synthetic polymer having at least 85 percent by weight of an ester of a substituted aromatic carboxylic acid unit, and a polypropylene fiber includes a long-chain synthetic crystalline polymer having at least 85 percent by weight of an olefin unit and typically having a number average molecular weight of about 40,000 or more.
The melt spinning process is of particular interest, since a large portion of the synthetic fibers that are used in the textile industry are manufactured by this technique. The melt spinning process generally involves passing a molten polymeric material through a device that is known as a spinneret to thereby form a set of individual synthetic fibers. Once formed, the synthetic fibers can be collected into a strand or cut into staple fibers. Synthetic fibers can be used to make knitted, woven, or non-woven fabrics, or, alternatively, synthetic fibers can be spun into a yarn to be used thereafter in a weaving or a knitting process to form a synthetic fabric.
Phase change materials have been incorporated into mono-component acrylic fibers to provide enhanced reversible thermal properties to the fibers themselves as well as to fabrics made therefrom. This is readily accomplished, in part due to the high levels of volatile materials (e.g., solvents) typically associated with the solution spinning process of forming acrylic fibers. However, it is more problematic to incorporate phase change materials into melt spun synthetic fibers, since high levels of volatile materials typically are not present or desired in the melt spinning process. Previous attempts to incorporate phase change materials into melt spun synthetic fibers typically involved mixing microcapsules containing a phase change material with a standard fiber-grade thermoplastic polymer to form a blend and subsequently melt spinning this blend to form mono-component synthetic fibers. Such attempts generally led to inadequate dispersion of the microcapsules within the fibers, poor fiber properties, and poor processability unless low concentrations of the microcapsules were used. However, with low concentrations of the microcapsules, the desired enhanced reversible thermal properties normally associated with use of phase change materials are difficult to realize.
It is against this background that a need arose to develop the multi-component fibers described herein.